1. Field of the invention
This invention relates to a signal-converting device for converting video signals output by a television camera or an electronic camera, thereby to change the size of the image formed of the video signals. More particularly, the invention relates to a signal-converting device suitable for use in a so-called "electronic zooming" device which processes an input signal to enlarge the image formed by the video signal, or a so-called "picture imposing apparatus" which processes the input video signal to reduce the image formed by the video signal, or a scanning line conversion apparatus which converts a video signal for a specific number of scanning lines to a video signal for a different number of scanning lines.
2. Description of the Related Art
Along with the advance in electronic technology, electronic cameras and video movie cameras (i.e., VTRs each having a built-in camera)--all for home use--are used in increasing numbers. It is demanded that the electronic cameras and the VTRs be modified so that they can be smaller and can be operated more easily. In most video movie cameras, zooming, i.e., one of the functions of the video movie camera, performed by operating a zoom lens. The use of a zoom lens, which is a relatively large component, has been an obstacle to the miniaturization of the video movie camera and the reduction in the weight thereof. Recently, a high-resolution solid-state imaging device has been developed, making it possible to achieve electronic zooming by processing the video signals generated by the imaging device. Hence, the video movie camera need not have a zoom lens, and can therefore be made smaller. A signal-converting device, which processes the video signals output by a solid-state imaging device, thereby to achieve electronic zooming, must be as simple as possible so that the video movie camera can be sold at so low a price that every household can buy it.
The signal-converting device used for achieving electronic zooming has the following problems, however.
First, when the signal-converting device processes the video signals such that the image formed of these signals is enlarged or reduced at a non-integral magnification, each component line of the original image may have a different thickness, depending on its location in the image. In other words, the enlarged or reduced image is noticeably distorted.
Second, the signal-converting device needs to have an A/D converter, a D/A converter and a memory since its main function is to process digital signals. These indispensable components are relatively expensive, and the video movie camera may be too expensive a home-use apparatus.
Further, the signal-converting device must have a circuit which can process the video signals output by the solid-state imaging device at high speed, thus within a limited period of time. This is because the video signals represents an image which is moving. The high-speed signal-processing circuit consumes much electric power.